In an attempt to reduce hydrocarbon emissions, environmental regulations in certain areas of the country require that gasoline vapors displaced from vehicle fuel tanks during refueling are to be recovered in order to prevent their escape into the atmosphere. Accordingly, nozzle assemblies incorporating vapor recovery systems have been designed to comply with these regulations. As is known in the art, many of these nozzles have a vapor-recovery system for receiving the vapors displaced from the fuel tank and storing them in a service station's underground hydrocarbon storage tank. These nozzles normally include a discharge spout that extends into the mouth of the fill pipe of the fuel tank and a vapor-recovery shroud that fits in sealing engagement with the mouth of the fill pipe during refueling so as to receive the vapors displaced from the fuel tank. With this arrangement, vapors in the fuel tank are displaced from the tank as gasoline is pumped into the tank. The displaced vapors will then flow by way of the shroud into a vapor-recovery passage in the nozzle and from there by appropriate means to a hydrocarbon storage tank.
Two problems that commonly arise in the use of vapor-recovery nozzles are the occurrence of spitback and spills. Spitback and spills may also occur when using fuel-dispensing nozzles not incorporating a vapor-recovery system; however, with these nozzles the problem is neither as severe nor the occurrence as frequent as with vapor-recovery nozzles. Spitback may be said to occur when a liquid spray is forcefully ejected from the fill pipe of a vehicle fuel tank when the nozzle is shut off and the flow of fuel into the tank is stopped. Spills may simply be defined as fuel that spills from the nozzle when the nozzle is removed from the fill pipe or that slops out of the fill pipe when the nozzle is shut off. Spitback and spills are undesirable in that they may strike the vehicle and/or the operator of the nozzle, and that they produce hydrocarbon emissions which offset the gain made towards the recovery of escaping vapors by the use of vapor-recovery nozzles.
When a vehicle is being refueled, and considering the fill-pipe geometries of various vehicle fuel tanks, it is likely that the discharge spout of the nozzle will be inserted into the fill pipe in such a way that fuel flowing through the outlet end of the discharge spout will initially strike the upper surface of the fill pipe. It can be expected that the fuel will strike the upper surface of the fill pipe with a high velocity and turbulent flow causing the fuel to flow along the upper surface and sides of the fill pipe. Downstream from the point where the fuel initially strikes the upper surface of the fill pipe, the fuel will drop from the upper surface of the fill pipe to its lower surface, establishing a liquid barrier in the fill pipe through which vapor displaced from the fuel tank must pass. The liquid barrier acts as an impediment to the flow of vapor through the fill pipe which leads to a buildup of vapor pressure in the ullage or head space of the fuel tank. A pressure differential is thereby established across the liquid barrier wherein the pressure in the head space of the fuel tank, which is downstream of the barrier, is greater than the pressure in the fill pipe near the point of insertion of the discharge spout, which is upstream of the barrier. Therefore, when the flow of fuel into the tank is stopped, vapor flow transients may occur while the pressures on opposite sides of the liquid barrier are equalizing. The sudden equalizations of pressures on opposite sides of the barrier, especially where there is a very high pressure differential across the barrier, can cause fuel to be forcefully ejected from the fill pipe which, as defined above, is known as spitback. The equalizations of the barrier pressures may also cause a spill to occur where fuel slops out of the fill pipe or flows into the nozzle where it can subsequently spill to the ground.
The formation of a liquid barrier in the fill pipe can also cause another problem known as recirculation. Recirculation can occur in vapor-recovery nozzles when fuel droplets are entrained in the vapor as it passes through the liquid barrier and carried into the vapor-recovery line, which connects the nozzle to the fuel dispenser. Fuel droplets entrained in the vapor and carried into the vapor-recovery system are undesirable for two reasons: first, the customer is charged for fuel that he did not receive, and second, entrained fuel droplets can separate out from the vapor causing a liquid trap to be formed in the vapor-recovery line which acts as a barrier to the flow of vapor through the line which, in turn, can cause a further build-up of vapor pressure in the tank head space. The higher pressure in the tank head space has the effect of increasing the likelihood of the occurrence of spitback.
Fuel dispensing nozzles that are currently available, such as those described in U.S. Pat. Nos. 4,060,110 and 4,058,149, do not eliminate the heretofore-described problems. Accordingly, the present invention is directed to a design for a discharge spout tip for a fuel-dispensing nozzle wherein liquid barrier formation in the fill pipe is either reduced or eliminated, thereby reducing the likelihood of the occurrence of spitbacks, spills and recirculation.